The present invention concerns an electrolyte solution used for a lithium secondary battery and the lithium secondary battery.
For power sources for use in mobile communication such as cellular phones or portable personal computers in recent years, reduction of size and increase of energy density (capacity) have been demanded more and more, and practical use of them in electric cars, hybrid cars utilizing electric power as a portion of driving power has been under progress. Further, with a view point of environmental protection, development has been progressed not only for the storage of midnight power but also for power source used for power storage in combination with solar cells and wind power generation. Under such a situation, while lithium secondary batteries have attracted attention, since the lithium secondary batteries are deteriorated in the charge/discharge efficiency by repeating charge/discharge, lithium secondary batteries with less aging deterioration of the battery performance have been demanded.
For example, Japanese Unexamined Patent Application Publication No. 2012-156087 discloses a non-aqueous electrolyte secondary battery having a negative electrode, a positive electrode, a separator, and a non-aqueous electrolyte in which the negative electrode contains an active material where deintercalation and intercalation of lithium ions proceed at 0.3 V or higher (vs. Li+/Li) and 2.0 V or lower (vs. Li+/Li), and an organic boron compound is contained in the non-aqueous electrolyte. Further, Japanese Unexamined Patent Application Publication No. 2010-251313 describes that the cyclic characteristic of a battery is improved by using a non-aqueous electrolyte containing at least one of carbodiimides, sulfate esters, and boron compound. Further, International Patent Publication No. WO2012/133556 discloses a lithium secondary battery using an electrolyte solution comprising a mixture of at least one solvent selected from carbonate esters and borate esters, LiBF4, and tri-iso-propoxy boroxine.
Japanese Unexamined Patent Application Publication No. 2012-156087 involves a possibility that an electric amount that can be taken out, that is, the battery capacity may be deteriorated by lowering of an electrode potential difference between the positive and negative electrodes to decrease the battery voltage, and decreasing the working range of the positive and negative electrodes. In Japanese Unexamined Patent Application Publication No. 2010-251313, when a carbodiimide is incorporated in the electrolyte solution, since charges are consumed for the decomposition of the carbodiimide, the initial capacity of the battery may possibly be reduced. Further, in the lithium secondary battery of International Patent Publication WO2012/133556, while charging is possible even at a high voltage by incorporation of tri-iso-propoxy boroxine, a battery having more increased initial capacity and improved cycle characteristic is demanded. Accordingly, increase of capacitance and suppression of aging deterioration of the battery were not sufficient according to the prior art.